Process and apparatus for recovering zinc



Dec. 23, 1958 G. E. ALDERSON ET AL 2,865,739

PROCESS AND APPARATUS FOR RECOVERING ZINC 2 Sheets-Sheet 1 Filed Dec.20, 1956 R. m n N d m mm mf mmwmd/ s uu AHWRWJ w E AH v. if? 0 m WWW H 665m: A w

Dec. 23, 1958 G. E. ALDERSON ET AL 2,865,739

PROCESS AND APPARATUS FOR RECOVERING ZINC Filed Dec. 20, 1956 2Sheets-Sheet 2 M IF INVENTOR. 9e E- Aldersan ugene glpod IMKGL m '-r'+0rn :35

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5 EdW/n 2,865,739 PROCESS AND APPARATUS FOR REKIUVERJING ZINC George E.Alderson, Eugene W. Wood, and Edwin A. Britney, Birmingham, Ala,assignors to i i. .5. Bullock, line, a corporation of DelawareApplication December 2t 1956, Serial N o. 629,594 3 Claims. (Cl. 75-88)This invention relates to a process and apparatus for recovering zincfrom waste products, such for instance as from dross resulting from zincplating operations and the like, or, as will be apparent, from manyother materials in which there is metallic zinc.

Heretofore in the art to which our invention relates, it has beencustomary to provide furnaces in which the zinc containing material wasplaced and heated. These furnaces were provided with a relatively largeopening in one upper part thereof to which was connected 2. con denser.Upon heating the material to the boiling point of zinc, the zincvolatilizes, passes over in gaseous form into the condenser there to becondensed back into metallic zinc. In the operation of suchfurnace-condenser systems, so far as we know there heretofore has beenno accurate way to determine just when the furnace was substantially outof zinc. That is to say, if the starting material contains severalmetals of different kinds which become red hot or molten in the furnace,it is-very difiicult to ascertain by any known temperature measurementsjust when the optimum point in zinc recovery has been reached. Thus, ithas been customary to operate the system at full heat for a certainarbitrarily determined number of hours and then to shut it down. it isreadily appreciated that there is a point, near the end of the zincrecovery cycle, at which is reached the point of diminishing return withrespect to cost of operation versus the value of the zinc recovered. Asstated, insofar aswe are aware there has been no previous, accurate,reliable means to determine just when this point has been reached.Consequently, there heretofore has been much waste of heat, time andlabor in the operation of these systems.

in view of the foregoing a prime object of our invention is to provide aprocess for operating zinc furnace-condenser systems which shall befully effective to determine the point in the heating cycle when thecost of continuing the system in operation is substantially equal to thereturn on the zinc then being recovered, whereby the system may be shutdown at the optimum time during the cycle of operation.

Another object of our invention is to provide a process of the characterdesignated in which the optimum shutting down time of thefurnace-condenser system is determined by sensing or reading atemperature corresponding to that in the condenser and, in accordancewith a predetermined variation in the condenser temperature, shuttingdown the system.

Another object of ourinvention is to provide a process of the characterdesignated in which the amount of heat carried over by the gaseous zincfrom the furnace to the condenser, in unit time, is the criterion ormeasurement which is used to determine when the furnace should be shutdown and the cycle ended.

A still further object is to provide a process ofthe characterdesignated in which the temperature reading used in determining the endof the cycle is read on the outside of the condenser, therebyeliminating the necesasars Patented Dec. 23, 1958 2. sity of having toinsert temperature measuring devices into tne corrosive gases andgaseous metals inside the condenser.

A rurtner object is to provide. apparatus of the char- .xcter designatedin which the condenser is provided with an outer metal shell and aninner refractory lining, a part of the shell being cutaway to expose asection of the lining, and there being placed adjacent the outer surfaceof the refractory lining a temperature responsive device for taking thetemperature measurements of the condenser.

Another object is to provide apparatus of the character designated inwhich the temperature measurement just mentioned is taken from a blockof metal which is held in physically closecontact with the outer surfaceof the condenser lining, and in which the temperature responsive deviceis imbedded or placed inside the metal block, thus eliminatingvariations in the temperature reading which might be occasioned byvariations in outside temperature.

Apparatus illustrating features of our invention and which is entirelysuitable for carrying out our improved process is illustrated in theaccompanying drawings forming a part of this applicationin which:

Fig. 1 is a side elevational view, partly broken away and in section andshowing a zinc furnace-condenser system to which our invention has beenapplied;

Fig. 2 is an enlarged detail sectional view taken gen erally along lineII-II of Fig. 1;

Fig. 3 is a detail sectional view taken generally along line Ill-Ill ofFig. 2;

Fig. 4 is an elevational view, with certain parts removed, and showingone of the time-temperature charts in place on the recording mechanismand as the chart appears at the end of a heating cycle; and,

Fig. 5 is a detail detached view of a signal indicating device which isresponsive to a fall in temperature, thus to indicate the end of thecycle.

Referring ,tothe drawings for a better understanding of our invention weshow in'Fig. 1 a somewhat standard form .of zinc recoveryfurnace-condenser system. The furnace is indicated generally by theletter A and the condenser generally by the letter B.

The furnace may be mounted on a main trunnion lit suitably supported inA frames 11. A quadrant gear 12 may be provided on the trunnion It) andthis gear may be in mesh with a gear 13 which may be rotated by a handwheel 14, thus to'tilt the furnace when the condenser is removed, aswill be explained. It will be understood that gas or other fuel issupplied to the furnace through a conduit 16 and that there are branchconduits 17 and 18 which lead to burners, one of at 19.

The condenser B isremovably coupled to communicate with an opening inthe furnace end by means of a transition pipe 21. The body ofth-econdenser B comprises an outer shell of metal 22 and an inner refractorylining 23. The condenser is provided with lifting eyes 24 and it may besuitably supported on an A frame 26 while connected to the furnace.

By reference particularly to Figs. 2 and 3 it will be seen that along aside of the condenser B we cut a hole 27 in the outer metal shell 22what rectangular portion of the outer surface of the refractory lining 2the opening,

which is indicated along the lower edges thereof, an L-shaped platehaving a horizontal bottom leg 28 and a vertical leg thus to expose asome-' We weld or otherwise secure in or the like. We prefer to insulatethis block by means of a layer of insulating material 33. It will benoted that the insulating material, which may be fiber glass or thelike, completely surrounds the sides and ends of the block except thatsurface thereof indicated at 34 which con acts the exposed outer surfaceof the inner lining 23.

The copper block 32 is provided with a bore 36 to re ceive a heatresponsive bulb 37. The bulb 37 is connected by the usual capillary tube38 to a time-temperature recording instrument indicated general y by thenumeral 39. The bulb casing 40 may be provided with a handle 40a bymeans of which the bulb may be inserted in and withdrawn from the block32. As will be understood and is quite standard in the art, theinstrument 39 com rises a holder 41 which is rotatable by means of asynchronous electric motor or other clock mech nism, not shown. Mountedon the holder are changeable pacer discs 42 which are laid out torepresent tem erature and hour readings as shown. The apparatus 39 isprovided with an inking pen for drawing the line 43 which has beenremoved from the drawing for the sake of clarity. The tube 38 isconnected in suitable manner to the inking pen so that the position ofthe pen radia'ly inward or outward of the chart varies in accordancewith the tem erature on the bulb.

As shown in Fig. the instrument 39 also may be equip ed with abellows-like expansible member 44 which actua es a switch having astationary contact 46 and a movable contact 47 carried by the bellows.This switch contr s the circuits shown in Fig. 5, whereby upon asuitable drop in the temperature below a predetermined m nimum a s nalmeans such as the incandescent light 470 is energi ed through the lines48 from a source of current. not shown.

From the foregoing the method of carrying out our improved orocesstogether with the method of constructing and using our improvedapparatus may now be explained and understood. With the furnace chargedwith material contain ng metallic zinc, such for instance as drossobtained from zinc using industrial processes, the condenser is put inplace as shown. The furnace is now fired bv su lying as through the line16 and the branch lines 17 and 18 to the burners. Curve 43 begins at43a. As the temperature in the condenser rises the curve commenees to bedrawn upon the disc 42 which is rotating in the di e ion of the arrow49. For instance, the temperature indicated bv bulb 37 on the condenserB may come u to around 500 F. within about an hour and a half after thecommencement of the firing of the furnace, mav rise to around 600? F.after about eight hours after the furnace is first fired, and then mayreach 700 F. after about eleven hours of the firing of the furnace. Thetem erature then will remain at approximately 700 F. for about 4 hours.At that time the temperature will commence to drop and, afterapproximately the 19th h ur the tem erature will have fallenapproximately 60 F. As has been stated, our invention is predicated uponthe concept that the heat being transferred from the furnace to thecondenser is taken over to the condenser by the gaseous zinc. Therefore,during the time that the condenser is coming up to temperature andduring that time that the condenser maintains its maximum temperature,about 700 F. on. the bulb 37, zinc is being transferred from the furnaceto the condenser in gaseous form. Heat thus is being transferred by thegaseous zinc from the furnace to the condenser. However, when thetemperature commences to fall from its maximum point, we have discoveredthat this indicates that the furnace is now commencing to run out ofmetal lic zinc. Further, we have discovered that after the temperaturefalls as much as about 40 F. to 80 F. as indicated by bulb 37, thesystem has reached the point of diminishing return, namely, has reachedthe point where the cost of continuing the system in operation exceedsthe value of the zinc being recovered. Therefore, that is the optimumtime to shut down the furnace, clean it out, and recharge it for a newcycle. In order to indicate this to the operator the signal light 47a isenergized by the closing of the switch 46-47 in response to the fall intemperature, telling the operator that the optimum time has come to shutdown the furnace.

From the foregoing it will be seen that our invention is especiallyadapted to save time in the operation of zinc recovery furnaces. Whilewe have specifically disclosed the use of our invention in associationwith the recovery of zinc, it will be apparent to those skilled in theart that there may be other instances in the recovery of metals and thelike in which our invention may have utility. Therefore, the disclosureof the invention for use in recovering zinc and the claim setting forththe recovery of zinc are intended to disclose and claim, respectively,the recovery of other metals and the like.

In actual practice and in the operation of tin zinc recovery systems ofthe kind shown herein our invention has proved extremely satisfactory.Through its use we have shortened the usual average cycle time fromabout twenty four hours to approximately twenty hours. It will beunderstood that in the operation of the system, the furnace is broughtup to temperature required to boil the zinc and is held substantially atthat temperature during the entire process. This is accomplished by theusual furnace temperature control means, not shown. Therefore, ourinvention is particularly useful in those types of volatilizationrecovery furnaces in which the gases are corrosive or the material isapt to deposit on the temperature indicating means, making itimpractical to place such means in the gases themselves. By cutting awaythe side of the shell to expose a part of the surface of the refractorylining we obtain a temperature reading which is substantially directlyproportional to the temperature existing in the condenser. Therefore,our improved process and apparatus employs a means for continuallysensing a temperature which is substantially constantly proportional tothe temperature existing within the condenser. It will be understood, ofcourse, that the temperature indicated on the chart is not thetemperature existing in the condenser. We therefore utilize an indirectbut proportional reading, lower than the actual temperature in thecondenser, to carry out our process.

Furthermore, by checking a series of charts 42 from an individualsystem, We can tell when the condenser walls become excessively coatedwith zinc dust, commonly called blue powder. This information is usefulin determining when the condenser lining must be freed of this coating.

in actual practice our invention has proved to be extremely satisfactoryin operation and has resulted in tremendous savings in the operation offurnaces of the kind indicated. By making a permanent record of eachcycle we are enabled to maintain a check on the operation of the systeminasmuch as the time, temperature, amount of fuel used and amount ofzinc recovered can be compared with the amount of zinc remaining in thefurnace after the furnace is shut down, thereby to keep check on thecost of the operation, cycle by cycle.

While we have shown our invention in but one form, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various changes and modifications without departing from the spiritthereof, and we desire, therefore, that only such limitations shall beplaced thereupon as are specifically set forth in the appended claims.

What we claim is:

1. The process of operating a zinc recovery furnacecondenser systemwhich comprises the steps of charging the furnace, bringing the furnaceup to zinc vaporizing temperature and holding it at said temperature,continuously sensing a temperature near the outer surface of thecondenser which is substantially proportionally constant to thetemperature inside the condenser, and shutting down the system when saidtemperature of the condenser falls a predetermined number of degrees inpredetermined time.

2. In a zinc condenser, an outer metal shell forming the outer surfaceof the condenser, an inner lining of ceramic material contacting theinner circumference of said outer shell, there being an opening in theshell exposing a section of the outer surface of the lining, a block ofmetal having heat transmitting properties on the order of those ofcopper contacting the exposed surface of said lining, means holding saidblock of metal in place on said lining, and a temperature responsiveunit inside said block of metal whereby heat is transmitted to said unitfrom the condenser through said inner lining and said block of metal.

3. Apparatus as defined in claim 2 in which the block is wrapped ininsulating material except on the side thereof contacting said lining,and signal means is operatively connected to said temperature unit andoperable upon a' predetermined drop in temperature as indicated by saidunit.

References Cited in the file of this patent UNITED STATES PATENTS1,301,011 Scoutten Apr. 15, 1919 1,585,451 White May 18, 1926 1,712,133Breyer May 7, 1929 1,901,543 Weaton Mar. 14, 1933 2,213,622 CarrawaySept. 3, 1940 2,282,441 Whitlock May 12, 1942 2,577,902 McGrath Dec. 11,1951 2,749,583 Loewenstein June 12, 1956 OTHER REFERENCES The Metallurgyof Zinc and Cadmium, by Walter Ren-

1. THE PROCESS OF OPERATING A ZINC RECOVERY FURACECONDENSER SYSTEM WHICHCOMPRISES THE STEPS OF CHARGING THE FURNACE, BRINGING THE FURNACE UP TOZINC VAPORIZING TEMPERATURE AND HOLDING IT AT SAID TEMPERATURE,CONTRINUOUSLY SENSING A TEMPERATURE NEAR THE OUTER SURFACE OF THECONDENSER WHICH IS SUBSTANTIALLY PROPORTIONALLY CONSTANT TO THETEMPERATURE INSIDE THE CONDENSER, AND SHUTTING DOWN THE SYSTEM WHEN SAIDTEMPERATURE OF THE CONDENSER FALLS A PREDETERMINED NUMBER OF DEGREES INPREDETERMINED TIME.